The technical field of this disclosure is power supplies, particularly, a power supply for LEDs.
Significant advances have been made in the technology of white light emitting diodes (LEDs). White light LEDs are commercially available which generate 10-15 lumens/watt. This is comparable to the performance of incandescent bulbs. In addition, LEDs offer other advantages such as longer operating life, shock/vibration resistance and design flexibility because of their small size. As a result, white light LEDs are replacing traditional incandescent sources for illumination applications such as signage, accenting, and pathway lighting. The white LEDs can be used alone or in conjunction with colored LEDs for a particular effect.
The existing power supplies for white light LED systems consists of a line frequency transformer for isolation and voltage matching, which feeds a rectifier/filter and a current limiting resistor, as shown in FIG. 1. The rectifier/filter converts the stepped down line ac voltage into dc voltage. The current limiting resistor regulates the LED current against variations in line voltage. The use of line frequency transformer makes the power supply bulky. The current limiting resistor causes power loss, making the power supplies inefficient. In addition, current regulation is not precise and differs for different LED string lengths (LEDs connected in series). The efficiency and current regulation could be optimized for a fixed number of LEDs in a particular light source, but then the power supply would only be suitable for that particular light source. Therefore, currently available power supplies are not capable of driving light sources with different number of LEDs (for example, one or more in a series string) with good regulation and efficiency.
The electrical characteristics of LEDs are such that small changes in the voltage applied to the LED lamp will cause appreciable current changes. In addition, ambient temperature changes will also result in LED current changes by changing the forward drop across the LEDs. Furthermore, the lumen output of LEDs depends on the LED current. The existing electrical power supplies for LED light sources are not designed to precisely regulate the LED current to prevent luminous intensity variations due to input ac voltage variations and ambient temperature. Operation of LED lamps at excessive forward current for a long period can cause unacceptable luminous intensity variations and even catastrophic failure. In addition, current electrical power supplies do not minimize power consumption to maximize energy savings.
It would be desirable to have a power supply for LEDs that would overcome the above disadvantages.
One aspect of the present invention provides a power supply for an LED light source with good regulation and efficiency.
Another aspect of the present invention provides a power supply for an LED light source able to drive variable numbers of LEDs.
Another aspect of the present invention provides a power supply for an LED light source able to accommodate the new generation of high power LEDs.
Another aspect of the present invention provides a power supply for an LED light source of small size and low weight.
Another aspect of the present invention provides a power supply for an LED light source protecting against open circuits and circuit malfunctions.
Another aspect of the present invention provides a power supply for an LED light source avoiding operation of LED lamps at excessive forward current.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.